[thstone]

Ok, its hard to hear, but if I had to guess, it sounds to me like the brake rotor is rubbing against the brake dust shield (or pebbles are stuck in between). My car will do this occasionally and it won't do it when the car is jacked up, only when its on the wheels and rolling. I removed the dust shields but you can just bend them back out of the way if this is the source of the sound.

Get a friend and find a local hill (just a slight decline) and let the car roll down the hill with the engine off and trans in neutral while someone walks next to the rear wheel to listen. Keep doing this several times until you find the cause.